This invention relates generally to gas turbine engines and more particularly to vane shrouds for use in such engines.
Gas turbine engines operate by combusting a fuel source in compressed air to create heated gases with increased pressure and density. The heated gases are ultimately forced through an exhaust nozzle, which is used to step up the velocity of the exiting gases and in-turn produce thrust for driving an aircraft. The heated gases are also used to drive a turbine for rotating a fan to provide air to a compressor section of the gas turbine engine. Additionally, the heated gases are used to drive a turbine for driving rotor blades inside the compressor section, which provides the compressed air used during combustion. The compressor section of a gas turbine engine typically comprises a series of rotor blade and stator vane stages. At each stage, rotating rotor blades push air past the stationary stator vanes. Each rotor/stator stage increases the pressure and density of the air. Stators serve two purposes: they convert the kinetic energy of the air into pressure, and they redirect the trajectory of the air coming off the rotors for flow into the next compressor stage.
The speed range of an aircraft powered by a gas turbine engine is directly related to the level of air pressure generated in the compressor section. For different aircraft speeds, the velocity of the airflow through the gas turbine engine varies. Thus, the incidence of the air onto rotor blades of subsequent compressor stages differs at different aircraft speeds. One way of achieving more efficient performance of the gas turbine engine over the entire speed range, especially at high speed/high pressure ranges, is to use variable stator vanes which can optimize the incidence of the airflow onto subsequent compressor stage rotors.
Variable stator vanes are typically circumferentially arranged between an outer diameter fan case and an inner diameter vane shroud. In split shroud designs, the vane shroud is divided into a forward and aft component, with inner diameter ends of the variable stator vanes secured between the two components. Traditionally, the forward and aft components of the inner diameter vane shroud have been fabricated from solid metal pieces. These solid metal vane shrouds are typically used in ground test engines where weight is not a concern. However, these solid vane shrouds are not suitable for use in production engines used in aircraft where weight is of the utmost concern. Thus, there is a need for a flight-weight inner diameter variable vane shroud.